The proposed research will study the continuity of behavioral and physiological reactivity over the perinatal period with special attention to the influence of labor variables and medical high risk factors as stress mediators. Adrenocortical activity will also be investigated. One theoretical assumption is that proper regulation of fetal adaptation is activated in preparation for postnatal life by the stress inherent in intrapartum uterine contractions. This conceptualization ascribes to labor, and other uterine contractions, the capability of enhancing or limiting optimal utilization of fetal resources. Thus, in terms of challenges that can be adaptively or maladaptively coped with by the fetus, uterine contractions are an excellent stimulus. Finally, the notion that temperamental patterns have constitutional roots with biological manifestations is central to the purpose of this research. Four hundred perinates will participate in this study, 200 normal, healthy, full-term AGA babies and 100 each from two perinatal high-risk groups-- term SGA and pre-term AGA. Prenatally, fetuses will be exposed to auditory stimuli presented through the maternal abdomen while cardiovascular and body movement activity is recorded. Dependent measures will include baseline data during periods of no stimulation as well as changes in measures evoked by stimulation. These measures will include fetal behavior, heart rate responses, and adrenocortical activity measured from umbilical cord blood. In the postnatal period, neonates will be administered a standardized neurobehavioral examination that will double as a mildly stressful stimulus to which adrenocortical activity changes can be measured. For comparison with prenatal stimulation, neonates will also participate in a heartrate habituation study from which measures of vagal tone will also be extracted. Mothers will be administered Questionnaires designed to assess their level of psychosocial stress. This data will be correlated with adrenocortical activity in the mother via assays for cortisol in saliva, along with the relationship of these measures to responses of their offspring. This research will explore perinatal responsivity within a hierarchical framework which includes assays of biochemical, physiological, behavioral and socially interactive functioning.